make compile command optional, fixes #505

bin/dartdevc.dart

@@ -57,6 +57,11 @@ Future main(List<String> args) async {
 Future<int> _runCommand(List<String> args,
     {MessageHandler messageHandler}) async {
   try {
+    if (args.isEmpty || args.first != 'compile' && args.first != 'help') {
+      // TODO(jmesserly): we should deprecate the commands. For now they are
+      // still supported for backwards compatibility.
+      args.insert(0, 'compile');
+    }
     var runner = new CommandRunner('dartdevc', 'Dart Development Compiler');
     runner.addCommand(new CompileCommand(messageHandler: messageHandler));
     await runner.run(args);

lib/src/compiler/code_generator.dart

@@ -5104,7 +5104,7 @@ String jsLibraryName(String buildRoot, LibraryElement library) {
         uri.path.substring(buildRoot.length).replaceAll('/', separator);
   } else {
     // We don't have a unique name.
-    throw 'Invalid build root.  $buildRoot does not contain ${uri.toFilePath()}';
+    throw 'Invalid build root. $buildRoot does not contain ${uri.toFilePath()}';
   }
   return pathToJSIdentifier(qualifiedPath);
 }

test/worker/worker_test.dart

@@ -163,7 +163,8 @@ main() {
     test('incorrect usage', () {
       var result = Process.runSync('dart', ['bin/dartdevc.dart', 'oops',]);
       expect(result.exitCode, 64);
-      expect(result.stdout, contains('Could not find a command named "oops"'));
+      expect(
+          result.stdout, contains('Please include the output file location.'));
       expect(result.stdout, isNot(contains('#0')));
     });